Mason Bald Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mason Bald Observatory clear sky chart from 2005-11-06 to 2024-01-27.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
31%
22780
15%
74978
8%
22737
39%
22737
17%
51973

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
16%
760
11%
2649
4%
757
26%
757
9%
2015
January11th to 20thNight
16%
760
8%
2650
3%
760
21%
760
8%
2097
January21st to endNight
20%
820
13%
2664
6%
820
29%
820
12%
1991
February1st to 10thNight
13%
720
10%
2340
2%
720
22%
720
10%
1793
February11th to 20thNight
16%
702
14%
2275
4%
700
29%
700
13%
1646
February21st to endNight
18%
592
15%
1830
5%
592
31%
592
14%
1305
March1st to 10thNight
22%
720
17%
2052
8%
720
31%
720
17%
1461
March11th to 20thNight
22%
720
16%
1979
6%
720
31%
720
18%
1417
March21st to endNight
27%
792
21%
2135
7%
792
37%
792
24%
1470
April1st to 10thNight
22%
720
17%
1800
4%
720
29%
720
22%
1300
April11th to 20thNight
27%
711
16%
1775
6%
711
32%
711
23%
1272
April21st to endNight
30%
586
16%
1666
7%
586
37%
586
21%
1159
May1st to 10thNight
36%
432
16%
1512
12%
432
42%
432
18%
996
May11th to 20thNight
38%
354
22%
1416
15%
354
55%
354
22%
815
May21st to endNight
44%
388
16%
1551
14%
388
55%
388
25%
870
June1st to 10thNight
38%
360
12%
1440
10%
360
50%
360
20%
880
June11th to 20thNight
44%
360
16%
1440
17%
360
54%
360
24%
830
June21st to endNight
47%
360
13%
1440
14%
360
55%
360
22%
870
July1st to 10thNight
54%
350
16%
1400
22%
350
61%
350
30%
734
July11th to 20thNight
54%
348
17%
1392
22%
348
60%
348
26%
786
July21st to endNight
55%
410
18%
1502
16%
388
61%
388
29%
823
August1st to 10thNight
60%
537
17%
1600
13%
534
63%
534
33%
963
August11th to 20thNight
58%
534
20%
1598
13%
534
63%
534
31%
981
August21st to endNight
50%
743
20%
1931
8%
743
56%
743
33%
1232
September1st to 10thNight
47%
720
17%
1800
7%
720
51%
720
33%
1173
September11th to 20thNight
55%
720
27%
1800
15%
720
60%
720
38%
1132
September21st to endNight
46%
720
21%
2072
16%
720
50%
720
26%
1357
October1st to 10thNight
37%
720
16%
2160
11%
720
44%
720
21%
1498
October11th to 20thNight
28%
720
13%
2160
8%
720
36%
720
18%
1562
October21st to endNight
22%
792
15%
2412
6%
792
33%
792
14%
1795
November1st to 10thNight
33%
740
18%
2455
14%
740
42%
740
19%
1619
November11th to 20thNight
23%
760
16%
2660
9%
760
34%
760
15%
1831
November21st to endNight
21%
760
11%
2660
5%
760
29%
760
11%
1957
December1st to 10thNight
16%
760
9%
2660
4%
760
24%
760
9%
2043
December11th to 20thNight
16%
759
10%
3247
4%
759
25%
759
8%
2383
December21st to endNight
12%
830
5%
4855
1%
817
20%
817
4%
3917

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
15%9%36%6%35%5%5%7%35%
74819
Night
17%9%36%5%35%5%5%7%35%
75221
TransparencyDay
47%7%13%20%11%1
74526
Night
48%7%12%20%11%1
75049
SeeingDay
20%15%31%21%10%3
13390
Night
21%12%31%26%10%1
22789

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
16%14%48%6%35%45%7%27%
1517
11th to 20thDay
16%18%6%8%6%4445%5%23%
1528
21st to endDay
14%14%5%10%8%5%5%5%5%5%24%
1836
February1st to 10thDay
14%15%5%10%8%35%5%6%6%22%
1620
11th to 20thDay
12%13%6%11%8%5%445%5%27%
1573
21st to endDay
20%13%5%9%6%445%36%26%
1424
March1st to 10thDay
15%10%48%7%45%5%5%6%30%
1903
11th to 20thDay
15%13%47%6%45%345%34%
1980
21st to endDay
20%10%36%5%34445%38%
2220
April1st to 10thDay
19%11%47%6%3445%6%33%
2160
11th to 20thDay
20%7%35%5%24346%40%
2134
21st to endDay
20%9%37%6%35%45%6%33%
2308
May1st to 10thDay
16%8%46%6%35%5%6%6%35%
2447
11th to 20thDay
14%6%35%5%35%5%5%7%41%
2478
21st to endDay
12%435%6%35%5%6%9%41%
2725
June1st to 10thDay
17%6%26%5%45%6%7%8%34%
2520
11th to 20thDay
13%5%25%5%35%5%7%10%40%
2520
21st to endDay
14%7%35%5%346%6%9%38%
2520
July1st to 10thDay
9%4345%35%6%6%9%45%
2520
11th to 20thDay
11%5%25%6%45%6%7%9%41%
2520
21st to endDay
9%5%25%6%47%7%8%9%38%
2726
August1st to 10thDay
9%6%35%5%35%7%6%10%41%
2327
11th to 20thDay
10%6%35%5%46%7%7%9%40%
2303
21st to endDay
12%5%25%5%35%6%6%9%42%
2406
September1st to 10thDay
12%5%35%5%35%5%7%8%43%
2160
11th to 20thDay
11%424425%46%8%50%
2160
21st to endDay
14%6%26%6%335%5%7%41%
1883
October1st to 10thDay
18%7%47%5%35%6%5%6%35%
1800
11th to 20thDay
19%9%36%6%45%5%6%6%31%
1800
21st to endDay
25%9%46%6%35%5%5%6%26%
1944
November1st to 10thDay
14%8%37%6%4446%7%35%
1619
11th to 20thDay
16%10%38%6%35%6%5%6%32%
1520
21st to endDay
21%11%47%6%35%5%5%6%26%
1520
December1st to 10thDay
18%15%6%9%7%45%436%23%
1520
11th to 20thDay
18%14%5%7%5%45%45%5%28%
1906
21st to endDay
29%14%47%6%34445%21%
2772
January1st to 10thNight
20%11%6%8%6%45%5%45%25%
2649
11th to 20thNight
19%13%5%10%7%46%5%45%23%
2650
21st to endNight
15%13%5%9%6%45%5%5%6%28%
2664
February1st to 10thNight
15%15%5%9%7%46%45%5%25%
2340
11th to 20thNight
15%12%5%8%6%35%5%6%6%29%
2273
21st to endNight
16%10%48%6%35%5%5%8%31%
1830
March1st to 10thNight
15%9%47%7%4446%6%34%
2042
11th to 20thNight
17%12%46%5%2445%6%35%
1979
21st to endNight
16%7%46%5%34445%41%
2135
April1st to 10thNight
19%8%46%5%3445%6%35%
1800
11th to 20thNight
18%7%37%5%3445%7%37%
1775
21st to endNight
19%6%27%5%346%6%7%35%
1666
May1st to 10thNight
19%6%35%5%35%5%6%7%37%
1512
11th to 20thNight
12%5%26%5%35%5%6%8%44%
1415
21st to endNight
10%5%245%345%7%7%48%
1550
June1st to 10thNight
14%5%35%6%36%46%9%39%
1440
11th to 20thNight
10%436%5%35%6%6%8%44%
1440
21st to endNight
12%7%35%6%445%5%7%43%
1440
July1st to 10thNight
6%5%15%5%35%5%5%9%52%
1440
11th to 20thNight
9%5%34435%6%6%8%47%
1440
21st to endNight
10%4245%345%6%8%49%
1590
August1st to 10thNight
8%6%25%5%3447%9%48%
1611
11th to 20thNight
8%426%4345%6%10%46%
1598
21st to endNight
8%5%35%5%35%5%6%9%46%
1931
September1st to 10thNight
11%5%25%5%3446%9%45%
1800
11th to 20thNight
12%4243245%5%7%53%
1800
21st to endNight
16%6%26%5%24447%44%
2072
October1st to 10thNight
17%6%46%5%445%6%7%37%
2160
11th to 20thNight
20%7%47%6%35%45%7%32%
2160
21st to endNight
22%8%47%6%45%447%29%
2412
November1st to 10thNight
19%7%35%5%345%5%7%39%
2455
11th to 20thNight
18%9%36%6%36%5%5%8%32%
2660
21st to endNight
21%10%36%5%45%5%6%7%28%
2660
December1st to 10thNight
21%12%5%8%6%35%5%5%6%25%
2660
11th to 20thNight
19%13%48%5%35%45%5%29%
3288
21st to endNight
30%14%47%5%345%5%5%17%
4884

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
56%7%13%17%7%1
1518
11th to 20thDay
63%7%9%11%10%
1528
21st to endDay
61%6%11%12%8%1
1836
February1st to 10thDay
62%7%11%14%5%1
1620
11th to 20thDay
58%6%10%14%10%2
1582
21st to endDay
59%6%11%14%9%1
1424
March1st to 10thDay
53%6%15%15%9%2
1906
11th to 20thDay
53%5%11%18%11%2
1980
21st to endDay
50%6%7%19%15%4
2220
April1st to 10thDay
52%5%10%19%11%3
2160
11th to 20thDay
47%410%22%16%2
2134
21st to endDay
51%6%10%18%13%2
2308
May1st to 10thDay
46%7%10%19%15%3
2447
11th to 20thDay
40%7%11%24%15%2
2482
21st to endDay
38%8%16%21%14%2
2725
June1st to 10thDay
44%8%14%19%14%1
2520
11th to 20thDay
37%8%14%24%14%2
2520
21st to endDay
40%9%15%22%13%1
2520
July1st to 10thDay
32%8%14%28%16%1
2450
11th to 20thDay
35%9%17%28%10%
2445
21st to endDay
37%10%17%25%11%1
2574
August1st to 10thDay
34%10%18%26%11%1
2314
11th to 20thDay
36%10%17%25%12%
2303
21st to endDay
35%8%16%28%11%2
2406
September1st to 10thDay
36%8%15%28%12%1
2160
11th to 20thDay
32%7%15%31%15%1
2160
21st to endDay
41%9%14%29%8%
1883
October1st to 10thDay
47%8%13%19%11%1
1800
11th to 20thDay
51%8%16%18%7%1
1800
21st to endDay
58%7%11%15%8%1
1944
November1st to 10thDay
46%7%17%19%10%1
1619
11th to 20thDay
50%9%15%17%10%1
1520
21st to endDay
57%9%13%13%8%
1520
December1st to 10thDay
62%7%13%13%5%
1520
11th to 20thDay
58%8%13%13%7%
1906
21st to endDay
66%7%10%12%5%
2772
January1st to 10thNight
61%6%11%15%7%
2649
11th to 20thNight
63%7%9%12%7%1
2650
21st to endNight
57%6%10%16%10%1
2664
February1st to 10thNight
61%6%11%16%5%1
2340
11th to 20thNight
55%5%12%19%9%
2275
21st to endNight
51%7%12%20%9%1
1830
March1st to 10thNight
50%6%12%19%11%2
2052
11th to 20thNight
50%6%11%20%12%1
1980
21st to endNight
46%5%8%22%16%4
2135
April1st to 10thNight
48%5%10%21%14%3
1800
11th to 20thNight
46%6%10%18%17%2
1775
21st to endNight
46%7%12%17%15%3
1666
May1st to 10thNight
45%7%9%18%17%3
1512
11th to 20thNight
37%6%12%25%17%4
1416
21st to endNight
33%8%15%20%19%4
1551
June1st to 10thNight
41%7%13%23%14%2
1440
11th to 20thNight
35%7%14%21%20%3
1440
21st to endNight
40%7%14%23%14%2
1440
July1st to 10thNight
28%8%13%25%24%2
1400
11th to 20thNight
34%8%12%29%16%
1392
21st to endNight
31%7%14%33%12%1
1502
August1st to 10thNight
32%8%17%30%13%1
1600
11th to 20thNight
33%9%16%27%14%2
1598
21st to endNight
32%10%13%30%15%1
1931
September1st to 10thNight
35%8%16%26%14%1
1800
11th to 20thNight
30%8%13%31%17%1
1800
21st to endNight
40%6%12%28%13%1
2072
October1st to 10thNight
45%8%11%21%14%1
2160
11th to 20thNight
51%6%14%21%8%
2160
21st to endNight
55%7%12%15%11%1
2412
November1st to 10thNight
44%7%13%23%12%1
2455
11th to 20thNight
49%8%13%18%10%2
2660
21st to endNight
53%10%16%15%5%1
2660
December1st to 10thNight
59%8%13%15%5%
2660
11th to 20thNight
57%7%13%16%6%1
3288
21st to endNight
69%7%11%10%4
4884

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
25%23%30%14%7%1
180
11th to 20thDay
28%22%32%15%31
184
21st to endDay
27%23%29%15%41
282
February1st to 10thDay
31%30%30%9%1
240
11th to 20thDay
25%26%39%8%1
240
21st to endDay
35%21%34%9%1
290
March1st to 10thDay
22%20%38%16%4
420
11th to 20thDay
25%20%33%18%3
420
21st to endDay
31%17%31%14%7%1
462
April1st to 10thDay
25%23%32%12%7%1
420
11th to 20thDay
26%21%25%17%9%3
412
21st to endDay
27%19%32%14%6%2
420
May1st to 10thDay
25%13%31%19%7%4
423
11th to 20thDay
18%11%35%23%9%3
447
21st to endDay
15%12%31%26%12%4
485
June1st to 10thDay
18%13%34%24%9%2
450
11th to 20thDay
13%13%32%26%13%4
450
21st to endDay
18%10%30%26%12%3
450
July1st to 10thDay
9%8%27%32%18%5%
445
11th to 20thDay
13%8%29%27%18%5%
444
21st to endDay
10%9%34%33%11%5%
488
August1st to 10thDay
10%6%31%29%17%7%
446
11th to 20thDay
12%5%26%31%20%7%
439
21st to endDay
12%8%31%26%14%8%
495
September1st to 10thDay
12%8%31%28%13%8%
450
11th to 20thDay
10%8%28%26%16%12%
450
21st to endDay
14%13%29%24%15%6%
450
October1st to 10thDay
21%16%25%18%14%6%
450
11th to 20thDay
23%19%32%18%7%2
450
21st to endDay
30%18%27%21%4
477
November1st to 10thDay
25%17%26%22%9%1
313
11th to 20thDay
24%22%34%16%31
180
21st to endDay
24%22%34%14%41
180
December1st to 10thDay
28%16%36%14%6%
180
11th to 20thDay
28%27%30%13%21
180
21st to endDay
36%19%32%12%2
198
January1st to 10thNight
27%18%30%20%4
760
11th to 20thNight
27%17%31%19%6%
760
21st to endNight
24%14%34%23%5%
820
February1st to 10thNight
23%18%39%18%2
720
11th to 20thNight
22%19%36%18%5%
703
21st to endNight
24%19%35%19%3
592
March1st to 10thNight
21%16%36%24%3
720
11th to 20thNight
23%17%33%22%41
720
21st to endNight
21%13%34%24%7%1
792
April1st to 10thNight
22%13%36%24%4
720
11th to 20thNight
21%15%32%22%9%1
711
21st to endNight
22%11%31%25%10%1
586
May1st to 10thNight
22%7%29%27%14%1
432
11th to 20thNight
14%7%36%33%10%
354
21st to endNight
11%5%34%33%15%1
389
June1st to 10thNight
15%436%32%13%1
360
11th to 20thNight
12%7%30%35%16%1
360
21st to endNight
13%5%28%38%15%1
360
July1st to 10thNight
5%6%27%42%19%1
350
11th to 20thNight
11%226%38%22%1
348
21st to endNight
10%228%43%17%1
410
August1st to 10thNight
11%319%39%25%3
537
11th to 20thNight
9%5%20%37%25%4
534
21st to endNight
10%428%35%22%2
743
September1st to 10thNight
13%5%28%32%19%3
720
11th to 20thNight
15%421%30%25%5%
720
21st to endNight
18%8%21%30%18%4
720
October1st to 10thNight
20%9%29%23%16%3
720
11th to 20thNight
24%13%30%25%8%1
720
21st to endNight
27%14%31%23%5%
792
November1st to 10thNight
23%14%25%28%9%1
740
11th to 20thNight
23%16%32%22%6%1
760
21st to endNight
28%15%31%19%7%
760
December1st to 10thNight
30%17%31%19%3
760
11th to 20thNight
25%18%34%19%4
760
21st to endNight
34%14%33%17%2
836
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Copyright 2024 Attilla Danko


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